Electric motor components which are used in motor vehicle applications, such as under the hood of an automobile or truck, are subject to water spraying, particularly when the vehicle is run through standing water in heavy precipitation. A particularly critical component is the electric motor driven fan assembly which forces cooling air through a radiator or other heat exchange device.
Conditions often require that the fan motor be directly exposed to water splashing into the engine compartment from the wheels, driven through the radiator or pulled through the radiator by the fan blades in heavy precipitation. Since the drive motors commonly have ventilating apertures which provide cooling air flow to the motor. The induction of water, particularly including road salts or other corrosive elements carried by the water, may be highly destructive to the steel cases, armature, laminations, the windings, commutator, brushes, and the motor bearings. The corrosive effects of road salts, for example, are greatly enhanced by the fact that the fan motor is normally operating at an elevated temperature due to the heat losses within the fan motor, engine temperatures, and the heat picked up by the air as it is drawn through the radiator. Such higher temperatures radically accelerate the effects of corrosion.
Fan motors can be totally sealed against intrusion of foreign matter, including water, but this is necessarily at the expense of having to provide much lower wattage rated motors, or much higher temperature rated materials, insulation, windings and the like and, for continuous operation, to provide a suitable means or heat sink for heat to be carried away from the fan motor itself. Therefore, it has become common practice to provide air circulation apertures in the end bell or end wall of the electric drive motor case at a position most closely adjacent the fan blade hub. When water is sprayed up from the wheels or is entrained in the air, it may enter the motor through the ventilating openings.